1. Field of the Invention
The present invention relates to an optical pickup and a disc drive apparatus. More particularly, the present invention relates to a technique for obtaining a large thrust for a focusing operation and reducing the thickness of a lens holder by attaching a first focusing coil and a second focusing coil to the lens holder in different orientations.
2. Description of the Related Art
In general, disc drive apparatuses are used for recording information signals on a disc-shaped recording medium, such as an optical disc and a magneto-optical disc, and reproducing the recorded information signals. The disc drive apparatuses include an optical pickup configured to move in a radial direction of the disc-shaped recording medium and irradiate the disc-shaped recording medium with a laser beam.
The optical pickup includes an objective-lens driving device, and the objective-lens driving device includes a fixed block and a movable block. The movable block is supported by a plurality of support springs, such as metal wires, which are fixed to the fixed block.
In the optical pickup, an objective lens is held by a lens holder provided on the movable block. Focus adjustment is performed by moving the movable block with respect to the fixed block in a focusing direction in which the movable block moves toward and away from a recording surface of the disc-shaped recording medium. In addition, tracking adjustment is performed by moving the movable block with respect to the fixed block in a tracking direction, which is substantially a radial direction of the disc-shaped recording medium. The focus adjustment and the tracking adjustment are performed such that the laser beam that is incident on the disc-shaped recording medium through the objective lens is focused to form a spot on the disc-shaped recording medium at a recording track thereof.
The objective-lens driving device provided in the optical pickup includes a focusing magnetic circuit for moving the movable block in the focusing direction and a tracking magnetic circuit for moving the movable block in the tracking direction. Each of the magnetic circuits includes a coil and a magnet.
In the objective-lens driving device, the movable block and the fixed block are connected to each other by the support springs such that the movable block and the fixed block are spaced from each other in a tangential direction, which is perpendicular to both the focusing direction and the tracking direction.
When the optical pickup is moved in the radial direction of the disc-shaped recording medium, the laser beam is guided to a rising mirror disposed below the objective lens through an optical-path opening formed in a surface of the lens holder that is opposite to a surface facing the fixed block. The laser beam is reflected by the rising mirror and is incident on the recording surface of the disc-shaped recording medium through the objective lens. In this state, the focus adjustment and the tracking adjustment are performed such that the laser beam that is incident on the disc-shaped recording medium through the objective lens is focused to form a spot on the disc-shaped recording medium at the recording track thereof.
An example of an objective-lens driving device of the related art is described in Japanese Unexamined Patent Application Publication No. 2007-102912. In this objective-lens driving device, focusing coils are attached to either side of the lens holder, which holds objective lens, in the tangential direction. The objective-lens driving device is structured such that the center (drive center) of thrust generated by the focusing coils and focusing magnets in the focusing direction coincides with the center of gravity of the movable block or the center of the objective lens.
The focusing operation is performed while the center of thrust coincides with the center of gravity of the movable block or the center of the objective lens. Consequently, unnecessary resonance can be suppressed and the reliability of the focusing operation can be increased.